Inverter with zener-regulated output frequency and voltage

ABSTRACT

A solid-state power supply for transforming unregulated direct current electrical energy into regulated alternating current and/or direct current electrical energy. The power supply has a common collector, DC to AC inverter with a circuit for limiting the excursion of the inverter drive voltage to prevent saturation of the common collector power transistors. The power transistors in the inverter function simultaneously as power oscillators and as series regulators. A shunt regulator is connected to a pair of diodes which in turn are connected to the power transistors for controlling the excursion of the base drive voltage. The inverter is connected to a transformer which provides one or more regulated AC outputs. Rectifier-filter circuits may be connected to the output of the transformer to provide regulated direct current electrical energy. A feedback network is connected from the output of the inverter to the shunt regulator to control the limiting voltage of the shunt regulator.

United States Patent 72] Inventor Donald A. Boelte'r Indianapolis, Ind.

[2!] Appl. No. 18,416

[22] Filed Mar. 11, 1970 [45] Patented Dec. 21, 1971 [7 3 AssigneeGeneral Aviation Electronics, Inc.

Indianapolis, Ind.

[54] INVERTER WITH ZENER-REGULATED OUTPUT FREQUENCY AND VOLTAGE 4Claims, 3 Drawing Figs.

[52] US. Cl 321/2, 321/18, 331/113 A [51] Int. Cl. ..I102m 7/52, H03k3/28 [50] Field ofSearch 321/2,18; 331/1 13.]

[56] References Cited UNITED STATES PATENTS 3,551,845 12/1970 ZelinaABSTRACT: A solid-state power supply for transforming unregulated directcurrent electrical energy into regulated alternating current and/ordirect current electrical energy. The power supply has a commoncollector, DC to AC inverter with a circuit for limiting the excursionof the inverter drive voltage to prevent saturation of the commoncollector power transistors. The power transistors in the inverterfunction simultaneously as power oscillators and as series regulators. Ashunt regulator is connected to a pair of diodes which in turn areconnected to the power transistors for controlling the excursion of thebase drive voltage. The inverter is connected to a transformer whichprovides one or more regulated AC outputs. Rectifier-filter circuits maybe connected to the output 3,192,464 6/1965 Johnson et al 321/23,335,316 8/1967 s h id 321 2 X of the transformer to provide regulateddirect current electri- 3,3s7,229 6/1968 Corey 331/1131 cal y- Afeedback network is connected from the output of the inverter to theshunt regulator to control the limiting voltage of the shunt regulator.

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ATTORNEYS AN INVERTER WITH ZONER-REGULATED OUTPUT FREQUENCY AND VOLTAGEBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an electrical power supply having power transistors whichsimultaneously function as series regulators and as power oscillators.

2. Description of the Prior Art A number of solid-state power supplieshave been developed in recent years. Generally the DC to AC powersupplies contain a standard saturated inverter circuit for convertingthe input DC electrical energy into AC electrical energy. These invertercircuits employ saturated power transistors which act as oscillators tochange the DC electrical energy into AC electrical energy. The netresult of utilizing saturated transistors is a low current gain,switching speed and circuit efficiency.

The inverter circuit is generally supplied regulated voltage by aseparate series regulator circuit having at least one highpowertransistor. The high-power transistor is very expensive and greatlyincreases the heat-sinking requirement.

From the above background it can be concluded that there is a need foran inverter circuit which operates in a nonsaturated mode. In addition,it is desirable for the inverter circuit to receive regulated voltagefrom a circuit based on a component other than a high-power transistor.These needs can be fulfilled by an inverter circuit having nonsaturatedoscillator transistors which simultaneously function as regulatortransistors. Thus, such a circuit would not require a separate seriesregulator circuit.

The present invention provides a power supply having an inverter whichis controlled by a shunt regulator circuit in lieu of the seriesregulator circuit. The oscillator transistors utilized in the inverterare operated in a nonsaturated mode providing a higher usable currentgain, switching speed and circuit efficiency. The oscillator transistorssimultaneously function as regulator transistors.

SUMMARY OF THE INVENTION The present invention is a power supply whichtransfonns unregulated direct current electrical energy into regulateddirect current and/or alternating current electrical energy. The powersupply has an inverter controlled by a shunt regulator in such a mannerthat the inverter transistors act simultaneously as regulators and aspower oscillators. The inverter transistors are connected in a commoncollector arrangement having their bases connected to the shuntregulator via a pair of diodes. The emitters of the inverter transistorsare connected across a first primary transformer winding while the basesof the inverter transistors are connected across a second primarytransformer winding. Feedback is provided to the shunt regulator.Regulated alternating current electrical energy is provided by theoutput terminals of the secondary transformer winding. Rectifier-filtercircuits are connected to the secondary winding of the transformer inorder to provide regulated direct current electrical energy.

It is one object of this invention to provide a power supply havinginverter transistors which operate simultaneously as series regulatorsand as power oscillators.

Another object of this invention is to provide a power supply havinginverter transistors connected to a-shunt regulator in such a mannerthat the excursion base voltages of the inverter transistors arecontrolled by the shunt regulator.

A further object of this invention is to provide a power supply havinginverter transistors operating in a nonsaturated mode allowing a highusable current gain, switching speed and efficiency.

Related objects and advantages will be apparent from the drawings,claims and the portion of the specification which follows.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a general block diagram of a powersupply incorporating the present invention;

FIG. 2 is a detailed schematic representation of the inverter shown inFIG. 1; and

FIG. 3 is a detailed schematic representation of a power supply based onthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is aunique method and device for generating one or more regulated AC or DCvoltages. An embodiment of the invention is a common collector DC to ACinverter connected to a circuit for limiting the excursion of theinverter base drive voltage. As a result, the inverter power transistorsare prevented from saturating. The inverter transistors functionsimultaneously as power oscillators and as series regulators providing avoltage-regulated drive to the inverter transformer. The transformerprovides one or more regulated AC output voltages. The transformeroutputs may be rectified and filtered to provide regulated DC voltages.

Referring now more particularly to FIG. 1, there is illustrated aninverter 9 having an input for receiving unregulated direct currentelectrical energy and an output for conveying regulated alternatingcurrent electrical energy. A shunt regulator 40 is shown connected toinverter 9 for limiting the drive voltage of inverter 9. Optionalcircuits are shown by dashed lines and dashed blocks. A feedback networkmay be connected between the inverter output and the input of shuntregulator 40 for applying the rectified inverter output energy tocontrol the limiting voltage of regulator 40. Rectifier-filter circuits58 may be connected to the inverter output to provide regulated directcurrent electrical energy.

FIG. 2 is a detailed schematic representation of the components used forinverter 9 shown in FIG. I. Inverter 9 receives unregulated directcurrent electrical energy from input terminals 10 and 11. Connected toterminals 10 and 11 is capacitor 12 for providing a low source impedanceto increase the switching speeds and efficiency of the circuit. Inaddition, terminal 10 is connected to the collectors of transistors 15and I6. Transistor 15 has its base connected to the anode of diode l3and to terminal 31 of the second primary winding 23 of transfonner 20.Transistor 16 has its base connected to the anode of diode l4 and toterminal 30 of second primary winding 23 of transformer 20. The cathodesof diodes 13 and 14 are connected together to zener diode 40 which inturn is connected to terminal 11. The emitters of transistors 15 and 16are connected respectively to terminals 28 and 29 of first primarywinding 21 of transformer 20. Terminal 10 is connected to the collectorsof transistors 15 and 16 and to resistor 17 which is connected to thecenter tap tenninal 24 of second primary winding 23 of transformer 20.Resistor l8 and capacitor 19 are connected in parallel between terminal11 and center tap terminal 24. In addition, the center tap terminal 22of first primary winding 21 of transformer 20 is connected to terminal 1l.

Transistors 1S and 16 are NPN-oscillator transistors connected in thecommon collector or emitter follower arrangement and will typically bemediumor high-power transistors. The starting bias for transistors 15and 16 isiprovided by resistors I7 and 18. Capacitor 19 provides a lowfeedback impedance to increase the switching speed and efficiency of thecircuit.

As is well known, the emitter voltage of a junction transistor may beregulated by controlling the base voltage. This is true since theemitter voltage of a junction transistor operated in a linear moderemains within 0.7:t0.2 volts of the base voltage over an extremely widerange of emitter current. Zener diode 40 limits the excursion of thebasedrive voltages of transistors 15 and 16 while diodes I3 and 14 providethe proper offset voltage to the transistor bases to insure that theemitter voltages equal the voltage determined by the shunt regulator.-

the base-emitter junctions. The shunt regulator may be a single-zenerdiode or as complex as utilizing the rectified output of the inverter tocontrol the limiting voltage of the shunt regulator as will be describedlater.

The operation of the circuit of FIG. 2 will now be described. A DCvoltage is applied through terminals and 11 to the biasing resistors 17and 18 applying base voltage to transistors and 16. Transistors 15 and16 will both turn on; however, the transistors are chosen so one willconduct more heavily than the other. For example, as transistor 15 firstconducts more heavily than transistor 16, then the voltage at terminal28 begins to increase positively causing the voltage at terminal 30 togo negative turning transistor 16 off. As the voltage at terminal 30increases negatively, then the voltage at terminal 31 goes positivethereby driving transistor 15 harder. The voltage at terminals 28 and 31continue to rise until the voltage at terminal 31 equals the zenervoltage of zener 40' plus the forward voltage drop of diode 13. The basevoltage of transistor 15 is then clamped. The emitter voltage oftransistor 15 is then also fixed as is the voltage at terminal 28. Zenerdiode 40' is chosen so that the voltage at terminal 28 is less than theinput DC voltage. The voltage at terminal 28 remains constant until thecore of transformer becomes magnetically saturated. The voltage atterminal 31 then drops towards zero point and the voltage at terminalincreases from a negative value to a positive value, transistor 16 willthen turn on with the transistor 15 turning off. Diode 14 will thenconduct and clamp the base voltage of transistor 16. The cycle isrepeated so as to alternatively turn transistors 15 and 16 off and on.Capacitor 19 increases the switching speed. The number of transformerturns on coil 21 as well as the core material of the transformer and thezener voltage determines the frequency of the output signal. Theamplitude of oscillation is not controlled by the transformer. The zenervoltage regulates not only the output frequency but also the outputvoltage.

Transformer 20 has a first primary winding 21, a second primary winding23 and a secondary winding 25 with output terminals 26 and 27 connectedacross the secondary winding. Transformer 20 may also have multiplesecondary windings depending upon the output voltages required. Thetransformer output may be rectified and filtered to provide regulateddirect current electrical energy.

Examples of components which have been successfully employed in theinverter circuit of FIG. 2 are as follows:

Capacitor I2 640 pF Capacitor 19 2.5 F

Diodes [3 k [4 l amp. 50 volt Transistors 15 a 16 40363 Resistor I7 330ohms Resistor I8 22 ohms Shunt Regulator IN 4740 zener diode FIG. 3shows, in addition to the inverter shown in FIG. 2, typical componentsfor shunt regulator 40 as well as typical circuits for rectifying andfiltering the output of transformer 20. As previously described, shuntregulator 40 is connected to the cathodes of diodes 13 and 14. Shuntregulator 40 could be a single-zener diode with its anode connected toterminal 11 and its cathode connected to the cathodes of diodes l3 and14. An alternate circuit for the shunt regulator is shown in FIG. 3. Thecathodes of diodes l3 and 14 are connected together to the emitter ofPNP-transistor 43 which has its base connected to resistor 44. Resistor44 in turn is connected to the collector of NPN-transistor 45 which hasits base connected to variable resistor 50. The collector of transistor43 is connected across resistor 46 to terminal 11. The emitter oftransistor 43 is connected across resistor 41, which is in series withvariable resistor and resistor 42, to terminal 11. The emitter oftransistor 45 is connected to terminal 51 in order that the rectifiedoutput of the inverter may be used to control the limiting voltage ofthe shunt regulator. Capacitor 47 is connected between terminal 11 andthe cathodes of diodes l3 and 14. Inductor 49 and capacitors 12 and 48are connected between the collector of transistors 15 and 16 and inputterminals l0 and 11.

Examples of components which have been successfully employed in theshunt regulator shown in FIG. 3 are as follows:

Capacitor 47 250 pF Capacitor I2 640 pF Inductor 49 50 all Resistors 4|a 42 i 2.2 K ohms Resistor 44 l K ohms Resistor 46 82 ohms VariableResistor 50 I K ohms Transistor 43 2N3638 Transistor 45 SE400l Alsoshown in FIG. 3 are the various rectifier-filter circuits 5 58 connectedto the output terminals 26 and 27 of the secondary winding 25 andterminals 30 and 31 of primary winding 23 of transformer 20.Rectifier-filter circuits 58 are standard circuits, several of which aredepicted in FIG. 3 for providing regulated direct current electricalenergy. Terminals 52 through 57 are connected at various pointsthroughout circuit 58 to provide various positive and negative outputvoltages. The rectifier-filter circuits will not be described, it beingunderstood that the circuits are obvious to one skilled in the art.

It will be evident from the above description that the present inventionprovides a method and apparatus for using inverter transistors in apower supply simultaneously as power regulator transistors andoscillator transistors. It will also be evident from the abovedescription that the present invention provides a method and apparatusfor using oscillator 0 transistors in a nonsaturated mode resulting in amuch higher usable current gain, switching speed and circuit efficiency.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restricted in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications which come within the spirit of the inventionare desired to be protected. Thus, the invention is not intended toencompass only specific circuits as illustrated, but the method of usingthe oscillator transistors simultaneously as power regulatortransistors.

The invention claimed is:

1. A solid-state power supply for converting unregulated direct currentelectrical energy into regulated electrical energy comprising:

a transformer with a pair of primary windings;

a pair of nonsaturating transistors having load paths connected togetheracross one of said windings and bases connected together across theother of said windings;

a zener diode with a first end connected to a common ground and with anopposite end; and,

a pair of diodes having second ends connected together to said oppositeend of said zener diode and third ends connected directly to said bases,said diodes limiting the maximum drive voltage of said bases to avoltage provided by said zener diode.

2. The power supply of claim 1 wherein:

said transformer has a maximum of two primary windings;

and,

said transistors have emitters connected together across one of saidprimary windings and collectors connected directly together, said basesare connected across the other of said primary windings.

3. The power supply of claim 2 wherein:

said primary windings have center tap terminals connected togetherthrough a first resistor and capacitor connected together in parallelarrangement; and further comprising:

a second resistor connected between said collectors and said center tapterminal of one of said primary windings.

4. The power supply of claim 3 wherein:

said first end of said zener diode and said third ends of said pair ofdiodes are anodes.

i i it 4 i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,629,682 Dated December 21. 1971 Inventor(s) Donald A. Boelter Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 47 change "zener diode 40" to --zener diode 40" Column 2,v 1 I.ne72 change -"zener diode 40" to --zener diode 40' O Signed andsealed this 13th day of June 1972.

(SEAL) Attest: v

EDWARD M.FLETCHER, JR. R0 BERT GOTTSCHALK Attesti-ng OfficerCommissioner of Patents USCOMM-DC 60376-P69 i 0.5. covlmmtm PIINI'INGorncr nu o-su-su "ORM PO-105O (IO-69) UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent NO- 3,629,682 Date December 21. 1971Inventor(s) Donald A. Boelter It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 47 change "zener diode 40" to --zener diode 40" Signedand sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesti-ng Officer 7Commissioner of Patents

1. A solid-state power supply for converting unregulated direct currentelectrical energy into regulated electrical energy comprising: atransformer with a pair of primary windings; a pair of nonsaturatingtransistors having load paths connected together across one of saidwindings and bases connected together across the other of said windings;a zener diode with a first end connected to a common ground and with anopposite end; and, a pair of diodes having second ends connectedtogether to said opposite end of said zener diode and third endsconnected directly to said bases, said diodes limiting the maximum drivevoltage of said bases to a voltage provided by said zener diode.
 2. Thepower supply of claim 1 wherein: said transformer has a maximum of twoprimary windings; and, said transistors have emitters connected togetheracross one of said primary windings and collectors connected directlytogether, said bases are connected across the other of said primarywindings.
 3. The power supply of claim 2 wherein: said primary windingshave center tap terminals connected together through a first resistorand capacitor connected together in parallel arrangement; and furthercomprising: a second resistor connected between said collectors and saidcenter tap terminal of one of said primary windings.
 4. The power supplyof claim 3 wherein: said first end of said zener diode and said thirdends of said pair of diodes are anodes.